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NORTHERN  HEMLOCK  AND  HARDWOOD 
MANUFACTURERS  ASSOCIATION 

Bulletin  1 

R.  B.  GOODMAN,  President 
O.  T.  SWAN,  Secretary 

In  Co-Operation  with  the 

Forest  Service 
U.  S.  Department  of  Agriculture 

HENRY  S.  GRAVES,  Forester 


The  Structure  of  Wood  and  Some 
of  its  Properties  and  Uses 


An  Address  Before  the  Members  of  the  Northern  Hemlock  and  Hardwood 

Manufacturers  Association,  at  the  Forest  Products 

Laboratory— April  28,  1915 


BY 


ELOISE  GERRY 

Microscopist,  Forest  Products  Laboratory 
Madison,  Wis. 


FORTKY 


OF&  AGrUCyi 


OSHKOSH,  WISCONSIN 
JANUARY,  1916 


NORTHERN  HEMLOCK  AND  HARDWOOD 
MANUFACTURERS  ASSOCIATION 

Bulletin  1 

R.  B.  GOODMAN,  President 
O.  T.  SWAN,  Secretary 

In  Co-Operation  with  the 

Forest  Service 
U.  S.  Department  of  Agriculture 

HENRY  S.  GRAVES,  Forester 


The  Structure  of  Wood  and  Some 
of  its  Properties  and  Uses 


An  Address  Before  the  Members  of  the  Northern  Hemlock  and  Hardwood 

Manufacturers  Association,  at  the  Forest  Products 

Laboratory— April  28,  1915 

BY 

ELOISE  GERRY 

i/ 
Microscopist,  Forest  Products  Laboratory 

Madison,  Wis. 


p*  out  rrr  *f*  0tV»f  toi 


FORESTRY 

s  Qf£iAG 


OSHKOSH,  WISCONSIN 
JANUARY,  1916 


ffio  •  V" 

The  Structure  of  Wood  and  Some  of 
Its  Properties  and  Uses* 

By  ELOISE  GERRY 

Microscopist,  Forest  Products  Laboratory,  Madison,  Wisconsin 


THE  STRUCTURE  OF  WOOD. 

A  microscopical  study  of  wood  brings  out  the  characteristics* 
by  which  different  kinds  of  woo  1  can  be  identified.  It  makes  clear 
many  of  the  reasons  for  the  variations  in  the  properties,  both 
chemical  and  physical,  and  for  the  behavior  of  wood  un:ler  differ- 
ent circumstances. 

Variability  of  \V<><i<l.  —  For  building1  purposes  wood  competes, 
for  instance,  with  tile,  brick,  steel,  and  other  inorganic  compounds* 
of  a  relatively  homogeneous  character.  Wood,  which  is  produced! 
by  the  growth  of  living  cells,  shows  marked  variations  in  its  struc- 
ture, due  to  the  conditions,  such  as  abundant  or  seanty  moisture, 
nutrition,  or  light  which  surround  the  individual  plant  during  its 
fcrijrition.  The  variations  found  among  different  pines,  oaks,  and 
maples,  are  striking,  but  besides  these  variations  within  the  genus 
(e.g.  pine,  oak,  maple)  these  woods  vary  so  widely  from  one  another 
that  each  may  be  said  to  represent  me  of  three  separate  groups  into 
which  all  woods  may  be  divided.  (£ee  Plates  I,  II,  and  III.) 


and  Ilearhrood.—  Besides  the  variations  in  minute 
structure  there  are  in  every  tree  two  regions  whieh  differ  markedly 
from  each  other.  These  are  the  sap  and  heart  wood. 

The  sapwood  is  the  layer  of  wood  on  the  outer  circumference  of 
the  tree  just  under  the  bark.  It  varies  in  different  trees  from  less 
than  one-half  an  inch  in  width,  for  example,  in  osage  orange  or  about 
an  inch  in  most  oaks,  to  five  or  more  inches  in  width  in  certain 
pines  such  as  loblolly.  The  sapwood  differs  from  the  heartwood 
because  it  contains  living  cells  and  the  functional  elements  which 
conduct  the  crude  sap,  that  is  the  water  and  dissolved  mineral  salts, 
from  the  roots  to  the  leaves.  In  the  leaves,  in  the  presence  of  the 
green  coloring  material,  callH  chlorophyll,  and  sunlight  this  crude 
sap  is  converted  into  the  elaborated  sap  which  provides  nourish- 
ment for  the  young  growing  tissue.  The  elaborated  sap  is  eon- 
ducted  down  the  tree  from  the  leaves  through  the  inner  layers  of 
the  bark.  From  here  it  is  distributed  to  the  growing  cells,  especially 
those  in  the  outer  sapwood. 

The  heartwood  which  occurs  around  the  pith  at  the  center  of  the 
tree,  does  not  contain  living  cells.  It  is  often  conspicuous  in  contrast 
to  the  light  colored  sapwood  by  reason  of  its  darker  color,  as  for 
example  in  red  cedar,  black  walnut,  and  ebony.  It  is  usually  more 
durable  than  the  sapwood.  Every  year  as  the  inner  sapwood  cells 
oease  to  function  they  add  a  little  to  the  width  of  the  heartwood 
at  its  outer  limit.  Therefore,  as  the  tree  grows  older  the  amount 

-  b°f0»<\il[he^niembor's    of    th('    X°rthern    Hemlock    and    Hardwood    Manufac- 
on,  at   the   Forest   Products   Laboratory—  April   28,    1915. 


of  heartwood  is  constantly  increased.  The  amount  of  sapwood  re- 
mains always  about  the  same.  The  sapwood  is  continually  recru-iteu 
on  us  outer  circumference  by  the  addition  of  new  ceils  formed  by  the 
cambium  or  growing  layer  which  is  located  between  the  wood  and 
the  bark.  This  is  the  layer  of  soft  thin-walled  cells  which  is  broken 
when  in  the  spring  the  small  boy  makes  whistles  by  slipping  the 
woody  cylinder  away  from  the  bark  on  a  willow  shoot. 

The  Annual  Rings.— In  temperate  climates,  like  that  of  the 
United  States,  the  tree  lays  down  a  yearly  increment  of  growth. 
This  is  produced  from  the  cambium  and  forms  the  outermost  layer 
of  the  sapwood.  This  addition  of  new  material  is  called  an  annual 
growth  ring,  ("ar"  Plate  I,  II,  and  III.)  The  age  of  a  tree  can 
be  estimated  with  considerable  accuracy  by  counting  these  rings. 

Opting  and  Summer  wood.  — The  part  of  the  annual  ring  which 
is  formed  early  in  the  season  is  called  the  springwood  ("Sp"  Plates 
I,  II,  III,  and  IV)  and  that  which  grows  later  the  summerwood .("S" 
Plates  I,  II,  III,  and  IV.)  The  trees  in  a  temperate  climate  cease 
growing  during  the  winter  months.  Springwood  cells  are  usually 
larger  in  diameter  and  have  thinner  walls  than  those  formed  later  in 
Ili«-  year.  The  summerwood  in  red  or  Norway  pine,  for  instance,  is 
the  hard,  somewhat  orange-colored,  conspicuous  portion  or  the 
"grain."  (cf.  Plate  I,  "S".) 

$oft  Woods  and  Hard  Woods. — The  so-called  softwoods  and 
hardwoods  are  not  divided  according  to  their  actual  hardness  in 
all  cases.  Therefore,  these  terms  which  are  so  commonly  used  are 
not  strictly  accurate.  For  example,  longleaf  pine  (Plate  1)  is 
harder  than  basswood  or  aspen  (Plate  II)  but  longleaf  is  regarded 
as  a  soft  wood  and  basswood  a  hard  wood  in  the  accepted  classifi- 
cation according  to  structure.  Softwoods  are  variously  known  as 
gymnosperms,  conifers,  and  non-porous  woods.  They  are  the  woods 
from  the  needle-leaved  trees  which  in  most  cases  (larch  and  cypress 
excepted)  are  "evergreens."  Plate  I  illustrates  woods  of  this  class. 
Hardwoods  are  known  as  angiosperms  and  porous  woods,  either 
diffuse  or  ring  porous,  according  to  the  arrangement  of  the  pores  in 
the  annual  ring.  These  woods  are  produced  by  the  broad-leaved 
trees.  On  the  whole  the  softwoods  have  a  much  simpler  structure 
than  the  hardwoods. 

Fibers  or  Tracheids. — The  elements  of  the  softwoods  are  chiefly 
fiber-like  cells  which  are  called  traclieids  ("t"  Plate  I).  These 
fibers  are  approximately  1/10  to  1/5  inches  long  and  have  tapering 
ends.  They  are  practically  closed  cells.  The  sap  passes  from  cell 
to  cell  through  thin  places  in  the  cell  wall  which  are  known  as 
bordered  pits.  The  thin  membranes  of  these  have  been  found*  in 
SBome  cases  to  contain  very  minute  perforations  which  assist  in  the 
passage  of  liquids  through  these  fibers.  On  the  whole,  however, 
the  elements  of  the  softwoods  may  be  said  to  lack  the  porous  type 
of  structure  which  assists  the  rapid  transfer  of  larae  quantities  of 
water,  such  as  exists  in  the  hardwood  trees.  For  this  reason  they 
are  called  non-porous  woods.  The  fibers  of  the  softwoods  are  placed 
end  to  end  in  the  tree.  The  ends,  however,  lap  each  other  approxi- 


*I.    W.    Bailey    "Preservative    Treatment    of   Wood."      For    Quar.    Vol.    XI,    No.    1, 
March,   1913. 

3 


477626 


inateiy  one-third  of  the  liber  length  and  the  fibers  run  parallel  to 
the  longitudinal  axis  of  the  tree.  The  sap  111  passing  up  a  comierous 
tree  zoo  feet  in  height  muse  tnen  traverse  approximately  3t>  —  f2,OUU 
of  the  fibers.  These  elements  serve  two  purposes,  viz.,  to  give  the 
required  mechanical  strength  to  hold  the  crown  of  leaves  up  into 
the  light  and  air,  and  also  to  conduct  the  crude  sap 'from  the  roots 
to  the  leaves. 

Medullary  Rays. — Other  important  elements  are  the  medullary 
rays.  (!See  4'mr  "  in  Plates  1,  li,  ill,  and  1V.J  These  are  made  up  01 
short  brick-shaped  cells.  Tlie  rays  extend  from  the  pitn  to  tiie  bant 
and  run  at  right  angles  to  the  longitudinal  axis  of  the  tree.  In  any 
cross  sectional  disc  from  a  tree  they  are  seen  to  extend  irom  the  pitn 
to  the  circumference  like  the  spoKes  in  a  wheel.  The  rays  are  much 
more  conspicuous  in  such  hardwoods  as  oak  or  beech  where  they 
produce  the  so-called  "silver  grain"  ("mr"  in  Hate  Iff)  than  they 
are  m  any  of  the  soft  woods.  The  medullary  rays  serve  to  conduct 
the  elaborated  csysmward  from  the  inner  bark  to  the  growing  por- 
tions of  the  sapwood. 

liesiti  uucts. — In  certain  softwoods,  viz.,  Douglas  hr,  spruce, 
larch  and  pine  we  lind  canals  here  and  there  among  the  cells,  ("re 
Hate  f.)  These  are  the  points  in  the  tree  where  the  resins  or  pitch, 
which  are  produced  by  these  species,  are  located.  They  are  01  con- 
siderable assistance  in  aiding  the  penetrance  of  a  wood  with  pre- 
servatives. They  extend  both  vertically  and  horizontally  through 
the  tree.  The  horizontal  canals  are  in  the  medullary  rays  and  are 
smaller  in  diameter  than  the  vertical  canals.  The  two  systems  fre- 
quently connect  with  each  other.  Among  the  important  soft  woods 
where  they  are  normally  absent  are  cedar,  hemlock,  balsam,  cypress, 
and  redwood.  The  American  hardwoods  do  not  have  resin  ducts 
but  in  addition  to  the  fibers  and  medullary  rays,  which  are  present 
in  both  hard  and  soft  woods,  they  possess  pores  or  vessels. 

Pores  or  Vessel  a. — These  elements  are  specialized  channels  which 
serve  to  conduct  the  ascending  stream  of  the  crude  sap.  They  may 
be  compared  to  the  water  pipes  which  extend  from  the  basement  to 
the  top  of  a  tall  building.  They  are  small  hollow  tubular  struc- 
tures. (See  "v"  Plates  ft,  III,  and  IV.) 

Diffuse  Porous  Woods, — If  the  pores  are  scattered  with  consider- 
able uniformity  through  the  annual  ring  and  there  is  relatively 
little  difference  in  size  between  those  in  the  springwood  and  those 
in  the  summerwood,  the  wood  is  said  to  be  diffuse  porous.  Maple, 
birch,  willow,  poplar,  basswood,  cherry,  gum  and  tulip  are  examples 
of  woods  belonging  to  this  class.  (See  Plate  II.) 

Ring  Porous  Woo ds.  —  When  there  is  a  considerable  difference 
in  size  between  the  pores  in  the  spring  and  those  in  the  summerwood 
and  the  large  pores  are  located  in  the  springwood  so  that  they 
form  conspicuous  concentric  rings,  as  seen  in  the  cross  section  of 
a  log,  the  wood  is  said  to  be  ring  porous.  Oak,  ash,  hickory,  elm. 
catalpa,  locust,  mulberry,  and  osage  orange  are  examples  of  woods 
belonging  to  this  class.  (See  Plate  III.) 

In  the  hardwoods  there  is  a  division  of  labor  among  the  ele- 
ments. The  fibers-  ("f"  Plates  II,  III,  and  IV),  which  jrive  the  im»- 

4 


ate  I. — A  Non-Porous  Wood.    Cross  Section  of  Longleaf  Pine;    AR,  annual  ring;   SP,  spring- 
wood;  S,  dense  summerwood;  T,  tracheids;  MR,  medullary  rays;  RC,  resin  canals. 


chanical  strength,  are  often  thick  walled.  They  frequently  have 
thicker  walls  in  proportion  to  the  lumen  or  cavity  enclosed  than  is 
found  in  the  softwoods.  They  also  share  little,  often  not  at  all,  in 
the  conduction  of  the  sap.  The  vessels,  on  the  other  hand,  are  ad- 
mirably constructed  to  assist  in  the  rapid  transfer  of  considerable 
quantities  of  water  solutions,  since  they  have  open  porous  ends 
which  facilitate  the  passage  of  liquids  with  greater  ease  and  rapidity 
than  the  tracheid  type  of  element,  where  the  passage  always  takes 
place  through  membranes,  even  though  these  may  be  thin  and  in 
some  cases  have  minute  perforations. 

Tyloses.— In  certain  hardwoods,  e.  g.  white  oak,  the  large  pores 
or  vessels  are  closed  more  or  less  completely  with  cell-like  growths 
called  tyloses  ("t"  Plate  IV).  These  in  many  cases  render  the 
wood  practically  impermeable  to  liquids  and  gases.  It  is  because 
of  the  presence  of  tyloses  that  white  oak  is  suitable  for  making 
liquid-tight  barrels  (tight  cooperage  stock).  Red  oak  lacks  these 
cells  and  cannot  be  used  for  liquid  containers  (it  is  classed  as  slack 
cooperage  stock).  This  lack  of  tyloses  makes  red  oak  (See  "V': 
Plate  III)  an  easy  wood  to  impregnate  with  preservative  solutions, 
such  as  coal-tar-creosote. 

Durable  hardwoods  as  a  rule  have  abundantly  developed  tyloses. 
Other  factors  such  as  chemical  composition,  rate  of  growth,  and 
hardness,  as  well  as  the  presence  of  tyloses,  are  however  also  signifi- 
cant in  determining  durability.  Tyloses  are  abundantly  developed 
in  the  following  very  durable  woods:  Black  locust,  catalpa,  osage 
orange,  mulberry,  white  oak,  post  oak  (Plate  IV)  and  red  heart 
beech.* 

In  the  species  where  tyloses  are  present  in  the  heartwood,  they 
are  found  more  or  less  fully  developed  in  the  sapwood  also.  In  the 
few  outside  annual  rings  where  the  sap  is  being  conducted  up  the 
tree  no  tyloses  are  normally  present.  Tyloses  may  be  said  to  act  as 
a  natural  filler  in  wood.  It  is  easier  for  a  carpenter  to  finish  white 
oak  than  red  oak,  for  the  tyloses  in  the  white  oak  provide  a  natural 
filler  to  catch  the  stain  and  varnish.  In  the  cases  of  penetrance 
treatments  and  the  water-logging  of  wood  tyloses  act  as  a  filler  or 
stopper  to  check  the  entrance  of  liquids.  In  the  same  way  they 
provide  a  barrier  to  the  entrance  of  wood-destroying  fungi,  the  or- 
ganisms causing  rot. 

THE  PROPERTIES  OF  WOOD  IN  RELATION  TO  ITS  USES. 

Chemical  Composition. — In  selecting  species  of  wood  for  special 
uses  it  is  important  to  consider  their  chemical  constitution.  Aside 
from  the  resins,  tannins,  and  other  special  secretions  peculiar  to 
the  different  species  of  wood,  the  bulk  of  the  wood  substance  is 
made  up  of  compounds  of  carbon,  hydrogen,  and  oxygen,  which  are 
chiefly  in  the  form  of  celluloses  and  lignin.  A  compound  which  has 
a  high  cellulose  content  is  well  adapted  to  the  production  of  a  high 
yield  of  chemical  pulp.  In  preparing  a  chemical  pulp  the  individual 
fibers  of  the  wood  are  separated  by  cooking  the  wood  in  a  liquor 
which  dissolves  out  the  greater  part  of  its  lignin  content.  This 


*See   Jour,   of   Agric.   Research,    Mar.    25,    1914.      Vol.    I,    No.    6.       "Tyloses:      Their 
Occurrence   and   Practical   Significance   in   Some   American   Woods." 


Plate  II.— Cross  Section  of  Poplar  or  Aspen.    A  Diffuse  Porous  Wood.     AR.  annual  ring;   SP, 
springwood;  S,  summer-wood;  F,  fibers;  MR,  medullary  rays;  V,  pores  or  vessels. 


leaves  the  separated  fibers  somewhat  thinner  and  weaker  but  with 
an  almost  pure  cellulose  composition,  similar  to  that  of  cotton  fibers. 
The  less  lignin  present  the  easier  it  is  to  separate  the  fibers  by  cook- 
ing. The  yield  of  pulp  secured  is  correspondingly  high  if  the  wood 
has  a  high  per  cent  of  celluloses  in  its  composition.  The  cellulose 
content  of  wood  is  also  important  in  the  production  of  ethyl  or 
grain  alcohol.  Spruce  is  an  example  of  a  wood  much  used  for  this 
purpose.  The  celluloses  present  in  the  sawdust  from  such  a  wood 
are  converted  into  sugar  by  treatment  with  acids.  The  solution  ob- 
tained is  then  neutralized  and  the  sugar  is  fermented  with  yeast, 
just  as  in  the  case  of  the  preparation  of  ethyl  alcohol  from  corn  or 
other  grains.  It  has  been  found  that  woods  with  a  high  lignin  con- 
tent give  an  especially  good  yield  of  wood  or  methyl  alcohol  in  the 
process  of  destructive  distillation.  Such  material  as  tops,  slabs  and 
edgings  are  used  for  this  purpose.  The  products  obtained  from  wood 
in  this  way  are  methyl  alcohol  (methanol),  acetic  acid,  and  char- 
coal. The  species  which  have  thus  far  been  most  successfully  used 
for  the  manufacture  of  these  products  are  beech,  birch,  and  maple. 

Physical  Properties.  — The  structure  and  mechanical  properties, 
such  as  strength,  hardness  and  toughness,  determine  the  suitability 
of  wood  for  particular  uses.  The  density  or  weight  of  the  wood 
bears  a  direct  relation  to  its  strength.  This  depends  upon  the  kind 
of  elements  present  and  the  way  in  which  they  are  arranged. 
Poplar  (Plate  II)  and  willow  have  many  large  open  pores  and  rela- 
tively thin  walled  cells.  Consequently,  they  are  weak  as  compared 
with  oak  (Plate  III)  or  black  locust  which  have  fewer  large  pores 
and  many  thick  walled  fibers  ("f"  Plate  III  and  IV).  It  has  been 
found  that  the  density  of  wood  substance  in  different  species  of  trees 
may,  for  practical  purposes,  be  considered  as  uniform  with  a  value 
of  1.54*,  yet  the  wood  substance  is  so  arranged  in  the  different 
species  that  the  unoccupied  space  in  a  block  may  often  be  from  two- 
fifths  to  four-fifths  of  its  volume.  The  arrangement  of  the  wood 
elements  under  these  circumstances  may  be  compared  with  that  of 
the  cells  in  a  honeycomb. 

The  openness  of  the  pores  and  the  uniformity  of  the  structure 
are  of  great  assistance  in  drying  a  wood.  For  this  reason  white 
pine,  spruce  and  birch  are  easier  to  dry  than  oak.  Water  is  con- 
tained in  wood  in  two  ways,— as  free  water  in  the  cell  cavities  and 
as  more  or  less  closely  combined  water  within  the  cell  walls  them- 
selves. It  is  a  relatively  easy  matter  to  dry  out  the  water  present 
in  the  cell  cavities  but  as  soon  as  an  attempt  is  made  to  remove  the 
water  within  the  cell  walls,  shrinkage  or  warping  begins  to  take 
place. 

Tradfl  Prejudices.— Trade  prejudices  which  are  maintained 
with  surprising  persistence  sometimes  hinder  and  sometimes  appar- 
ently assist  the  utilization  of  a  wood. 

It  has  been  found  that  many  of  the  soft  woods,  such  as  tam- 
arack, hemlock,  balsam,  and  jack  pine,  may  be  used  for  making 
ground  wood  pulp  for  newspaper  and  fiber  board  stock.  Some  of 
these  woods  do  not  produce  a  news  sheet  that  is  as  white  as  that 

*See   Journal   of   Agricultural    Research,    September   21,    1914,    Vol.    II,    No.    (>.      Tin- 
Density   of   Wood    Substance   and   the    Porosity   of   Wood — by    Frederick    Dunhip. 


te  III.— Cross  Section  of  Red  Oak.    A  Ring  Porous  Wood.    AR,  annual  ring;  SP,  springwood  (la 
open  pores);   S,  summerwood;  F,  fibers;  MR,  wide  medullary  ray  (silver  grain); 

V,  pores  or  vessels 


obtained  from  spruce.  The  slight  degree  of  difference  in  color 
would  not,  however,  interfere  with  the  legibility  of  the  printed 
words  and  the  average  reader  would  probably  not  notic'e  the  diff- 
erence, yet  the  prejudice  remains. 

It  is  a  well  known  fact  that  the  sale  of  small  cream  cheeses  is 
better  when  they  are  exhibited  in  white  basswood  boxes  than  when 
in  pasteboard  or  other  containers. 

Hickory  is  one  of  the  most  important  American  woods.  It  is 
remarkable  because  it  possesses  to  such  a  degree  the  combined 
properties  of  hardness,  weight,  stiffness,  and  toughness.  The 
hickory  wagon  spokes  and  rims  have  made  possible  the  American 
type  of  spring  wagon  with  its  superior  lightness  and  strength.  65 
per  cent  of  the  hickory  cut  is  made  into  vehicle  stock  and  handles. 
Approximately  one-half  of  this  is  used  for  spokes  for  wagon  and 
automobile  wheels.  The  hickory  handle  has  helped  to  make  the 
American  axe  known  all  over  the  world.  It  has  been  found  in  the 
intensive  studies  of  this  wood  made  by  the  Forest  Service  that  the 
red  heartwood  of  hickory,  which  was  once  largely  wasted,  is  fully  as 
valuable  for  handles,  etc.,  as  the  white  hickory.  The  trade  preju- 
dice in  favor  of  the  white  hickory  is  being  gradually  overcome. 
This  means  a  closer  utilization  of  this  valuable  wood.  A  significant 
step  in  this  line  is  the  adoption  by  the  United  States  Navy  Depart- 
ment of  a  hickory  handle  specification  which  admits  red  hickory  on 
the  same  terms  as  white.  A  structural  feature  which  influences  I  bo 
strength  of  hickory  to  a  marked  degree  is  the  width  of  the  annual 
rings.  Slow  growth  material  of  this  species  is  frequently  brash  and 
weak,  due  to  the  fact  that  when  a  ring  is  narrow  the  porous  struc- 
ture is  developed  at  the  expense  of  the  fiberous  portion  of  the  ring 
which  gives  the  strength  to  the  wood. 

Gmin  find  Te.rture.  —  The  terms  ''grain"  and  "texture"  are 
often  confused  and  misunderstood  in  present  usage.  The  distinc- 
tive application  of  each  has  been  well  given  as  follows* : 

"Grain  is  a  general  term  used  in  reference  to  the  arrange- 
ment and  direction  of  the  wood  elements  and  to  the  relative 
width  of  the  growth  rings.  To  have  specific  meaning  it  is  es- 
sential that  it  be  qualified.  Coarse  grain  applies  to  woods  of 
rapid  growth,  that  is,  it  denotes  wide  rings;  fine  grain  to  woods 
of  slow  growth.  Straight  grain  as  applied  to  a  tree  occurs  when 
the  wood  elements  are  parallel  to  the  axis  of  growth."  (The 
pine  in  Plate  I  has  a  finer  grain  than  the  oak  in  Plate  III  be- 
cause it  shows  three  complete  annual  rings  to  the  one  shown  in 
the  oak.) 

"Texture  is  a  term  which  refers  to  the  relative  size,  quality, 
or  fineness  of  the  elements.  Like  grain  it  requires  qualifying 
adjectives  to  attain  specific  meaning.  The  most  common  attri- 
butes of  texture  are  fineness  and  coarseness;  evenness  and  un- 
cvenness.  Coarse  texture  applies  to  woods  with  many  large  ele- 
ments (See  Plate  III  Oak)  or  the  average  size  of  which  is  large. 
For  example,  chestnut  and  sequoia.  In  fine  texture  the  oppo- 
site condition  prevails,  as  in  red  cedar  and  poplar.  (Plate  II.) 
Even  texture  or  uniform  texture  are  terms  used  to  describe 
woods  whose  elements  exhibit  little  variation  in  size,  for  ex- 

10 


Plate  IV.— Radial  Section  (Quarter  Sawed)  White  Oak.     A  Ring  Porous  Wood.     T,  tyloses 
(completely  closing  pores  or  vessels);  AR,  annual  ring;  Sp,  springwood;  S,  summer- 
wood;  F,  fibers;  MR,  medullary  ray;   V,  pores  or  vessels. 


11 


ample,  cedar  or  poplar.  (Plate  II.)  Uneven  texture  applies  to 
the  opposite  condition  such  as  is  common  in  all  prominently 
ring  porous  woods  (for  example  oak  (Plate  III),  elm  and  ash), 
and  in  other  woods  with  decided  differences  between  early  and 
late  wood  (for  example  long-leaf  pine  (Plate  I)  and  Douglas 
fir).  The  distinctions  as  above  expressed  will  obviate  the  diffi- 
culty resulting  from  the  attempt  to  make  the  term  "grain"  too 
comprehensive." 

CONCLUSION. 

Approximately  52,800,000,000  board  feet  of  wood  are  cut  annual- 
ly in  the  United  States.  This  is  enough  to  make  a  board  walk  two 
inches  thick  and  five  feet  wide  which  would  reach  approximately 
forty  times  around  the  earth  at  the  equator.  The  annual  cut  of 
wood  is  estimated  to  be  three  times  the  amount  of  the  annual 
growth  of  the  forests.  A  better  knowledge  of  wood  is  necessary 
to  insure  a  closer  and  more  advantageous  utilization  of  the  trees 
cut.  This  must  be  brought  about  by  the  widespread  co-operation  of 
all  those  interested  in  forest  products  whether  land  owners,  lumber- 
men, or  users  of  the  hundred  and  one  commodities,  from  gunpowder 
to  silk  neckties,  which  are  prepared  from  wood.  A  general  knowl- 
edge of  the  structure  of  wood  is  of  great  importance.  A  thorough 
knowledge  of  its  minute  structure  is  of  fundamental  significance  in 
the  solution  of  the  problems  which  are  continually  arising"  as  the 
work  of  better  utilization  progre^se«.  The  "open  sesame"  to  this 
knowledge  is  found  in  the  use  of  twro  commonplace  instruments, — 
the  "jack-knife"  and  the  "reading  glass"  or  small  hand  lens. 
Highly  perfected  modifications  of  these  which  greatly  assist  the 
more  careful  and  minute  study  of  wood  structure,  are  the  microtome, 
which,  by  means  of  a  very  sharp  razor,  cuts  sections  of  wood  one- 
five-thousandths  of  an  inch  in  thickness,  and  the  microscope  by 
which  these  sections  may  be  seen  greatly  magnified  in  size. 

It  is  like  opening  a  closed  book  to  read  the  history  of  the  life 
processes  of  the  tree  from  these  thin  transparent  sections  where  it  is 
possible  to  look  through  a  single  layer  of  the  elements  or  cells  which 
compose  the  wood.  It  often  seems  that  the  book  is  as  difficult  to 
understand  as  if  it  were  written  in  a  foreign  language,  but  by  dint 
of  study  and  experiment  much  of  the  meaning  and  the  relationships 
of  the  structural  elements  has  been  made  clear  and  this  information 
is  fast  being  made  available  for  all.  This  stivlv  revels  not  only  the 
wonderful  perfection  and  the  beantv  of  the  once  living  tissue  so 
useful  to  mankind  after  the  tree's  life  is  over,  but  it.  also  makes  ar>- 
parent  the  underlying  reasons  for  the  behavior  of  the  wood  sub- 
stance. On  the  results  of  snch  scientific  and  thorough  stndv  it.  is 
possible  to  lay  the  foundation  for  the  conservation  or.  in  other 
words,  the  efficient  practical  utilization  of  our  forest  resources. 


*S»e    S.    J.    Ro«-«H's    "Economic    Woods    of    tin-    United    Stjitos."    .1.    Wiley    #    Sons. 
Publishers. 


12 


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REC'D  L 

A:<  25 


Gaylord  Bros. 

Makers 
Syracuse,  X.  Y 

PAT.  JAM.  21. .1901 


YC  13692 


477626 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


